The present invention relates to a laminate organic resin wiring board and a method of producing the same and, more particularly, to a laminate organic resin wiring board consisting of a plurality of laminate blocks adhered together, and a method of producing the same.
Today, a laminate wiring board having a ceramic substrate and polyimide resin intervening between nearby layers for an insulation purpose is used as a wiring board for a large scale computer that needs dense wiring. It has been customary to produce this kind of polyimide-ceramic laminate wiring board by the steps of forming a polyimide resin insulating layer on the ceramic substrate, and forming wiring by photolithography, vacuum deposition, and plating. To form the polyimide resin insulating layer, polyimide precursor varnish is applied to the substrate and dried, and then via holes are formed in the resulting polyimide film. The above steps are repeated to produce a laminate polyimide wiring layer.
Another conventional method produces a laminate polyimide wiring board by dividing the substrate into a plurality of blocks, as taught in Japanese Patent Laid-Open Publication No. 5-206643 (Prior Art 1) by way of example. In Prior Art 1, a plurality of blocks produced beforehand are adhered together in order to complete the laminate wiring board. This kind of method is also disclosed in Japanese patent Laid-Open Publication No. 4-152694 (Prior Art 2). The difference between Prior Art 1 and Prior Art 2 is that while the former uses metal bumps for the electrical connection of wiring layers, the latter uses via holes for the same purpose.
However, Prior Art 1 and Prior Art 2 both have the following problem left unsolved. In Prior Art 1 and Prior Art 2, two laminate blocks each has a ground or feed layer, a polyimide insulating layer, a signal layer, a polyimide insulating layer, a ground or feed layer and a polyimide insulating layer sequentially laminated from the bottom to the top. The polyimide insulating layers or top layers of the laminate blocks are adhered to each other. The wiring board therefore needs a great number of layers. It follows that an increase in the number of layers directly translates into an increase in the period of time necessary for the production of the wiring board.